1. Field of the Invention
This invention relates to a water soluble packaging film containing an acetalized product of polyvinyl alcohol, and more particularly to a water soluble packaging film which is suitable for use as a packaging film of alkaline or acidic materials such as soaps, laundry detergents, bleaching agents, agrochemical and industrial chemicals.
2. Description of the Prior Art
Polyvinyl alcohol (hereinafter abbreviated as PVA) is generally soluble in cold water when the degree of hydrolysis is in the range of 80-90 mole %. However, it has been well known that PVA becomes insoluble in cold water when the degree of hydrolysis exceeds 90 mole %. Besides there is a problem in packaging of alkaline materials such as soaps or acidic chemicals such as aluminum sulfate, therein even if PVA in the film has a degree of hydrolysis of 80-90 mole %. In such cases, hydrolysis reaction of PVA proceeds during the storage with the passage of time, and cold water solubility of the film is lost when the degree of hydrolysis exceeds 90 mole %.
Therefore it has practically been impossible to use PVA based water soluble films for packaging the aforesaid chemicals. Consequently packaging films are required which exhibit stable water solubility independently of the alkaline and acidic chemicals. In addition, a film which can be removed at the development stage by dissolving in an alkaline or acidic solution is desired for the application to surface protecting films of photosensitive dry film resists developed in the alkaline or acidic solution.